The invention relates to assessing cardiac electrical stability.
Sudden cardiac death may result from disturbances of electrical conduction in the heart. A great majority of sudden cardiac deaths result from ventricular fibrillation, a disorganized pattern of electrical activity in the ventricles of the heart that leads to a disorganized pattern of mechanical contraction and results in the cessation of effective pumping action. Another disturbance of heart conduction processes, ventricular tachycardia, also reduces the effectiveness of the pumping action of the heart. Ventricular tachycardia can degenerate into ventricular fibrillation.
Sudden cardiac death may be prevented by identifying individuals at risk. It has been determined that alternans, a subtle beat-to-beat change in the repeating pattern of an electrocardiogram (ECG) waveform, can be indicative of electrical instability of the heart and increased susceptibility to sudden cardiac death. Alternans is an ABABAB . . . pattern of variation of waveform shape between successive beats in an ECG waveform. The level of alternans characterizes an individual's cardiac electrical stability.
The physiologic signal underlying an ECG waveform may be obtained through electrodes attached to a patient's chest. Typically, the electrodes include an electrically conductive gel that contacts the patient's skin and detects electrical signals produced by the patient's heart. The detected signals are then transmitted to ECG circuitry for processing and display.